This invention relates to the field of two-way communications equipment, and more particularly to the capability of transmitter-receiver switching with minimum noise output, and channel selection with minimum noise during "receive" and power amplifier protection during transmit.
Most mobile two-way communications equipment utilizes the depression of a "push-to-talk" switch, which is typically located on a hand-held microphone, to initiate transmission. Depression of the PTT switch keys up the transmitter and cuts off the receiver; when the switch is released, the transmitter is turned off and the equipment returns to "receive" mode. Also, most such equipment has the capability of operating on any one of a number of channels. Since the equipment is likely to be used in some type of emergency situation, the latter capability usually makes it possible for the user to locate an unused channel as needed. However, both of these switching functions, as well as other switching circuitry, can cause objectionable noise in the audio output. Channel switching during "transmit" can also cause damage to the transmitter power amplifier and its related circuitry. Therefore, a need exists for a means of eliminating such noise and providing circuit protection without adding unnecessary cost or complexity to the equipment.